• 10 parts
  • Checked September 2026

Parts of a Transformer

A simple step-up transformer, then an oil-filled power transformer.

Parts of a Transformer

Name Date

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1 2 3 4 5 6 7 8 9 10
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Write the name of each numbered part.Answer key

  1. Iron core
  2. Primary coil
  3. Secondary coil
  4. Input
  5. Output
  6. Conservator
  7. High-voltage bushings
  8. Low-voltage bushings
  9. Tank
  10. Radiators

Drawn for this site by script, 2026-09-27. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

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All 10 parts on the diagram

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Start here: 5 main parts 5

  1. Iron core Carries the magnetic field from one coil to the other. A ring of thin iron plates, laminated to cut wasted eddy currents.
  2. Primary coil The input voltage goes into this coil, or winding. Its changing current makes a changing magnetic field in the core.
  3. Secondary coil The output voltage is made in this coil, or winding. The changing field in the core makes it. More turns than the primary steps the voltage up.
  4. High-voltage bushings Tall insulators that carry the high-voltage wires into the tank. Made of porcelain or polymer.
  5. Tank Holds the core and coils in oil. The oil insulates and cools them.

Simple transformer: 5 2

  1. Input Wires from the alternating current (AC) supply to the primary coil. A transformer needs AC. Steady DC makes no output.
  2. Output Wires from the secondary coil to what it powers, here a bulb.

Power transformer: 5 3

  1. Conservator A small oil reservoir on top. It lets the oil level rise and fall as it warms and cools.
  2. Low-voltage bushings The low-voltage bushings: shorter insulators for the low-voltage side.
  3. Radiators The hot oil circulates through them to shed heat. Also called cooling fins.

How this list was compiled: Read 2026-09-27. (1) OpenStax, College Physics 2e, section 23.7 Transformers, https://openstax.org/books/college-physics-2e/pages/23-7-transformers : two coils, the primary and secondary, wound on a ferromagnetic core laminated to minimise eddy currents; the input voltage goes on the primary and the secondary gives the output; the core traps and strengthens the primary’s field and carries it to the secondary; the output voltage depends on the ratio of turns; step-up and step-down transformers; no change in the primary, no voltage in the secondary. (2) Wikipedia, Transformer, https://en.wikipedia.org/wiki/Transformer : windings on a core; cores made of laminations insulated from each other to reduce eddy currents; oil-filled transformers insulate and cool the windings and core with mineral oil circulating in the tank; the tank often has radiators or fins; the conservator (reservoir) on top copes with changes in oil level and temperature; larger transformers have high-voltage bushings of polymer or porcelain, and low-voltage bushings. Licence: own work

The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work

How it works

These are the parts of a transformer: first the simple transformer of a physics class, then an oil-filled power transformer like those at a substation. Start with the 5 main parts.

Read the full guide

How it works

Alternating current in the primary coil makes a changing magnetic field. The iron core carries it to the secondary coil, where it makes the output voltage. More turns on the secondary step the voltage up; fewer step it down.

A power transformer

The core and coils sit in oil inside the tank, which cools and insulates them. Hot oil runs through the radiators, the conservator on top holds spare oil, and bushings carry the wires in.

  • Compare the turns: this secondary has twice as many as the primary, so the output voltage is twice the input.

Questions and answers

What are the main parts of a transformer?

An iron core and two coils of wire wound on it: the primary, which takes the input, and the secondary, which gives the output. Big ones add a tank of oil, radiators and bushings.

Why is a transformer core laminated?

It is built from thin iron plates insulated from each other instead of one solid block. That cuts the eddy currents that would waste energy as heat.

Does a transformer work with DC?

No. It needs a changing current in the primary. Steady direct current makes a steady field, and a steady field makes no voltage in the secondary.

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